The invention relates to an annealable layer system with a transparent substrate, preferably a glass substrate, and a first layer sequence which is applied to the substrate directly or is applied to one of more bottom layers which are deposited on the substrate. The layer sequence comprises a substrate-proximal blocking layer, a selective layer, and a substrate-distal blocking layer.
The invention also relates to a method for producing an annealable layer system, where in said method a first layer sequence is applied to a transparent substrate, preferably a glass substrate, either directly to the substrate or to one of more bottom layers which are deposited on the substrate. The layer sequence therein comprises a substrate-proximal blocking layer, a selective layer, and a substrate-distal blocking layer.
The customary blocking layers, which comprise silver layers(s) (for example, an NiCr or NiCrOx layer, cf. patents DE 035 43 178 and EP 1 174 379) or offer protection at least on one side, lead to a reduction of the conductivity of the silver layers(s). If a silver layer with a conductivity of ca. 5 ohm/sq. is deposited and this is embedded in two NiCrOx layers, then this embedding can lead to an increase of the conductivity by ca. 1.5 ohm/sq. to 6.5 ohm/sq.
In EP 0 999 192 B1 a layer system is described which comprises a silver layer as a selective layer which is provided on both sides with a blocking layer of nickel or nickel chromium. These blocking layers protect the sensitive silver layer against being affected by neighboring layers. Along with this, the layer system is stabilized during the heat treatment by inserting an NiCrOx layer into the functional silver layer with a single low-E [coating]. The disadvantage consists in the fact that in this layer system each individual silver partial layer must be ca. 7 to 8 nm thick in order to avoid the formation of islands of the silver partial layers. This leads to a low transmission for the layer system. Furthermore, in EP 0 999 192 B1 the use of a substoichiometric TiOx layer between the blocking layer and the silver layer is described, which is intended to reduce the formation of haze. This absorbing TiOx layer oxidizes during the heat treatment, wherein significant changes of transmission and a shift of the preset color location take place.
In this realization several layer sequences of sensitive silver layers with bottom layers and each with two blocking layers enclosing the respective silver layer are also provided.
In practice, annealable layer systems are frequently required, i. e. layers which after application are subjected once again to a heat treatment, for example, in order to harden or bend them. The layer represented in EP 099 192 B1 [sic] does not exhibit such ability to be annealed since the blocking layers, as they are represented therein, are not sufficiently resistant to diffusion processes so that, during the annealing, materials from neighboring layers can diffuse into the silver layers, which leads to undesirable changes in color [so that] the color location of the layer system cannot be kept stable.
In EP 1 238 950 A2 an annealable layer system is described which provides on both sides of a silver layer, as a sensitive layer, NiCrOx layers as blocking layers. Furthermore, in this layer system, dielectric intermediate layers are provided which are located both above and below the blocking layers. Layers of this type also act as diffusion barrier during the annealing processes.
Furthermore, in EP 1 238 950 the use of gradient layers in the stabilization of heat-treated layer systems is described. The disadvantage therein consists in the fact that the SiNx layer lies below the blocking layer, whereby the resistance, and thus the emissivity of the layer system, is not reduced.
It has been shown that layer constructs of this type are sensitive to climatic conditions so that under demanding climatic conditions these layer systems cannot be produced with a sufficient quality or yield. Also in the case of rough glass with undefined initial properties, this layer system exhibits quality problems in manufacture.